AFI conformance test suite

Substrate-level gate: same @client fixture registered in both backends
emits equivalent schemas, therefore the codegen produces equivalent
TypeScript regardless of which backend the frontend is generated against.
Catches adapter symmetry problems (Pydantic→OpenAPI converter divergence,
metadata leakage, ordering non-determinism) without docker, browser, or
Playwright.

What ships:

backends/mizan-fastapi/src/mizan_fastapi/schema.py — build_schema():
- Builds OpenAPI 3.0 from registered Mizan functions, mirroring the
  shape mizan-django's export emits.
- Drives FastAPI's native OpenAPI generation by registering a stub POST
  endpoint per function with its Input/Output Pydantic models, then
  appends x-mizan-functions and x-mizan-contexts extensions.
- Param-elevation logic mirrors mizan-django/src/mizan/export/__init__.py
  exactly (sharedBy tracking, required iff every function in context has
  the param).
- snake_to_camel and metadata field shapes match Django for byte-equality
  on the AFI surface.

tests/afi/ — the conformance harness:
- fixture.py: 5 @client functions covering the protocol axes (plain,
  context, mutation+affects). No channels/forms — those aren't AFI-common.
- django_app/: minimal Django project (settings, urls, AppConfig.ready
  registers the fixture). manage.py adds tests/afi/ to sys.path so both
  backends import the same fixture module.
- fastapi_app.py: thin make_app() that registers fixture and mounts router.
- schema_normalizer.py: drops backend-specific framing — Ninja-vs-FastAPI
  envelope differences (info/servers/tags), Django-only function fields
  (form metadata), x-mizan-channels. Plus afi_subset() and
  function_io_schemas() helpers for narrower comparisons.
- test_codegen_parity.py: three gates
  1. x-mizan-functions match across backends
  2. x-mizan-contexts match across backends
  3. Per-function Input/Output OpenAPI schemas match (what codegen feeds
     to openapi-typescript for type generation)

The full normalized OpenAPI envelopes do diverge — FastAPI adds
HTTPValidationError, the two converters wrap things slightly differently
in non-AFI-essential ways. That's not in the test scope. The codegen
only consumes x-mizan-functions, x-mizan-contexts, and the per-function
type schemas; those are what the test gates.

Makefile: test-afi target added; rolls into the test aggregate.

Verified: 3/3 conformance tests pass. Other surfaces unaffected —
mizan-core 15/15, mizan-django 348 pass, mizan-fastapi 11/11.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backends/mizan-fastapi/src/mizan_fastapi/__init__.py

@@ -35,6 +35,7 @@ from .executor import (
     execute_function,
 )
 from .router import router, mizan_exception_handler, mizan_validation_handler
+from .schema import build_schema
 
 __all__ = [
     "router",
@@ -42,6 +43,7 @@ __all__ = [
     "mizan_validation_handler",
     "execute_function",
     "compute_invalidation",
+    "build_schema",
     "ErrorCode",
     "MizanError",
     "NotFound",

backends/mizan-fastapi/src/mizan_fastapi/schema.py

@@ -0,0 +1,209 @@
+"""
+Mizan schema export for FastAPI backends.
+
+Builds an OpenAPI 3.0 document from the registered Mizan functions, mirroring
+the shape mizan-django emits via Django Ninja so the codegen consumes either
+backend identically.
+
+Usage:
+    from mizan_fastapi.schema import build_schema
+    schema = build_schema()                # uses globally registered functions
+"""
+
+from __future__ import annotations
+
+import re
+from typing import Any
+
+from fastapi import FastAPI
+from fastapi.openapi.utils import get_openapi
+from pydantic import BaseModel, create_model
+
+from mizan_core.registry import get_all_functions, get_context_groups, get_function
+
+
+__all__ = ["build_schema", "snake_to_camel"]
+
+
+# Common user identity param names — mirrors mizan-django's _USER_SCOPED_PARAMS
+_USER_SCOPED_PARAMS = {"user_id", "user", "owner_id", "account_id"}
+
+
+def snake_to_camel(name: str) -> str:
+    """Convert snake_case or dotted.name to camelCase. Mirrors mizan-django."""
+    components = re.split(r"[._]", name)
+    return components[0] + "".join(c.title() for c in components[1:])
+
+
+def _has_input(input_cls: Any) -> bool:
+    return (
+        input_cls is not None
+        and input_cls is not BaseModel
+        and hasattr(input_cls, "model_fields")
+        and bool(input_cls.model_fields)
+    )
+
+
+def _annotation_to_jsonschema_type(annotation: Any) -> str:
+    if annotation is int:
+        return "integer"
+    if annotation is float:
+        return "number"
+    if annotation is bool:
+        return "boolean"
+    return "string"
+
+
+def _function_metadata(name: str, fn_class: Any) -> dict[str, Any]:
+    """Build one entry of x-mizan-functions. Mirrors Django's shape exactly."""
+    camel = snake_to_camel(name)
+    meta = getattr(fn_class, "_meta", {})
+
+    input_cls = getattr(fn_class, "Input", None)
+    has_input = _has_input(input_cls)
+
+    entry: dict[str, Any] = {
+        "name": name,
+        "camelName": camel,
+        "hasInput": has_input,
+        "inputType": f"{camel}Input" if has_input else None,
+        "outputType": f"{camel}Output",
+        "transport": "websocket" if meta.get("websocket") else "http",
+        "isContext": meta.get("context", False),
+        # Form metadata — always emitted so the schema shape matches Django's,
+        # even for FastAPI projects that don't use forms (these stay False/None).
+        "isForm": meta.get("form", False),
+        "formName": meta.get("form_name"),
+        "formRole": meta.get("form_role"),
+    }
+
+    if meta.get("affects"):
+        entry["affects"] = meta["affects"]
+
+    return entry
+
+
+def _context_metadata(context_groups: dict[str, list[str]]) -> dict[str, Any]:
+    """Build x-mizan-contexts. Mirrors Django's param-elevation logic."""
+    out: dict[str, Any] = {}
+
+    for ctx_name, fn_names in context_groups.items():
+        param_info: dict[str, dict[str, Any]] = {}
+
+        for fn_name in fn_names:
+            fn_cls = get_function(fn_name)
+            if fn_cls is None:
+                continue
+
+            input_cls = getattr(fn_cls, "Input", None)
+            if not _has_input(input_cls):
+                continue
+
+            for field_name, field_info in input_cls.model_fields.items():
+                if field_name not in param_info:
+                    param_info[field_name] = {
+                        "type": _annotation_to_jsonschema_type(field_info.annotation),
+                        "sharedBy": [],
+                    }
+                param_info[field_name]["sharedBy"].append(fn_name)
+
+        # A param is required iff every function in the context declares it.
+        for p_meta in param_info.values():
+            p_meta["required"] = len(p_meta["sharedBy"]) == len(fn_names)
+
+        out[ctx_name] = {
+            "functions": list(fn_names),
+            "params": param_info,
+        }
+
+    return out
+
+
+def build_schema() -> dict[str, Any]:
+    """
+    Build an OpenAPI 3.0 schema for all registered Mizan functions.
+
+    Drives FastAPI's native OpenAPI generation by registering a stub endpoint
+    per function with the function's Input/Output Pydantic models, then
+    appends the protocol's `x-mizan-functions` and `x-mizan-contexts`
+    extensions.
+
+    Returns a dict in the same shape mizan-django's schema export emits, so
+    the same codegen pipeline consumes either.
+    """
+    functions = get_all_functions()
+    context_groups = get_context_groups()
+
+    schema_app = FastAPI(
+        title="mizan Server Functions",
+        version="1.0.0",
+        description="Auto-generated schema for mizan server functions",
+    )
+
+    # Per-function endpoints + renamed Pydantic models so component names are
+    # camelCase + "Input"/"Output" rather than the user's original class names.
+    schema_classes: dict[str, type[BaseModel]] = {}
+    function_metadata: list[dict[str, Any]] = []
+
+    for name, fn_class in functions.items():
+        camel = snake_to_camel(name)
+        input_cls = getattr(fn_class, "Input", None)
+        output_cls = getattr(fn_class, "Output", None) or BaseModel
+        has_input = _has_input(input_cls)
+
+        input_type_name = f"{camel}Input" if has_input else None
+        output_type_name = f"{camel}Output"
+
+        if has_input:
+            schema_classes[input_type_name] = create_model(
+                input_type_name, __base__=input_cls,
+            )
+        schema_classes[output_type_name] = create_model(
+            output_type_name, __base__=output_cls,
+        )
+
+        # Stub endpoint — only exists so FastAPI walks Pydantic types into
+        # components.schemas. Never invoked. Annotations are set explicitly
+        # rather than via closures so forward-ref resolution doesn't trip on
+        # locally-bound type names.
+        if has_input:
+            async def stub(payload):
+                return None
+
+            stub.__annotations__ = {"payload": schema_classes[input_type_name]}
+        else:
+            async def stub():
+                return None
+
+        schema_app.post(
+            f"/mizan/{name}",
+            response_model=schema_classes[output_type_name],
+            operation_id=camel,
+            summary=fn_class.__doc__ or f"Call {name}",
+        )(stub)
+
+        function_metadata.append(_function_metadata(name, fn_class))
+
+    schema = get_openapi(
+        title=schema_app.title,
+        version=schema_app.version,
+        description=schema_app.description,
+        routes=schema_app.routes,
+    )
+
+    schema["x-mizan-functions"] = function_metadata
+
+    if context_groups:
+        schema["x-mizan-contexts"] = _context_metadata(context_groups)
+
+    # Attach x-mizan operation metadata, mirroring Django.
+    paths = schema.get("paths", {})
+    for fn_meta in function_metadata:
+        op = paths.get(f"/mizan/{fn_meta['name']}", {}).get("post")
+        if op is not None:
+            op["x-mizan"] = {
+                "transport": fn_meta["transport"],
+                "isContext": fn_meta["isContext"],
+            }
+
+    return schema